Theoretical and Numerical Studies on the Coupling Deformation of Global Lateral Buckling and Walking of Submarine Pipeline

Buckling initiation devices/techniques,including sleepers,distributed buoyancy,snake lay,and residual curvature method(RCM),have recently been widely applied in engineering.These initiated buckles may induce a long pipeline to transform into multiple short pipeline segments,which promote the occurrence of pipeline walking.Thus,a pipeline,which is designed to buckle laterally,may laterally and axially displace over time when subjected to repeated heating and cooling cycles.This study aims to reveal the coupling mechanism of pipeline walking and global lateral buckling.First,an analytic solution is proposed to estimate the walking of pipeline segments between two adjacent buckles.Then,the sensitivity of this method to heating and cooling cycles is analyzed.Results show the applicability of the proposed walking analytical solution of buckling pipelines.Subsequently,an influence analysis of walking on global buckling,including the capacity of buckling initiation,buckling amplitude,buckling mode,and failure assessment of the buckling pipeline,is performed.The results reveal that the effect of walking on the buckling axial force is negligible.However,pipeline walking will aggravate the asymmetry of the pipeline buckling and the failure parameters of the pipeline during the post-buckling.

Lateral Global Buckling of Submarine Pipelines Based on the Model of Nonlinear Pipe–Soil Interaction

With the increasing development and utilization of offshore oil and gas resources, global buckling failures of pipelines subjected to high temperature and high pressure are becoming increasingly important. For unburied or semi-buried submarine pipelines, lateral global buckling represents the main form of global buckling. The pipe–soil interaction determines the deformation and stress distribution of buckling pipelines. In this paper, the nonlinear pipe–soil interaction model is introduced into the analysis of pipeline lateral global buckling, a coupling method of PSI elements and the modified RIKS algorithm is proposed to study the lateral global buckling of a pipeline, and the buckling characteristics of submarine pipeline with a single arch symmetric initial imperfection under different pipe–soil interaction models are studied. Research shows that, compared with the ideal elastic–plastic pipe–soil interaction model, when the DNV-RP-F109 model is adopted to simulate the lateral pipe–soil interactions in the lateral global buckling of a pipeline, the buckling amplitude increases, however, the critical buckling force and the initial buckling temperature difference decreases. In the DNV-RP-F109 pipe–soil interaction model, the maximum soil resistance, the residual soil resistance, and the displacement to reach the maximum soil resistance have significant effects on the analysis results of pipeline global buckling.

Buckling of a sandwich symmetrical circular plate with varying mechanical properties of the core

This paper is devoted to analytical and numerical studies of global buckling of a sandwich circular plate. The mechanical properties of the plate core vary along its thickness, remaining constant in the facings. The middle surface of the plate is its symmetrical plane. The mathematical model of the plate is presented. The field of displacements is formulated using the proposed nonlinear hypothesis that generalizes the classical hypotheses. The equations of equilibrium are formulated based on the principle of stationary total potential energy. The proposed mathematical model of the displacements considers the shear effect. The numerical model of the plate is also formulated with a view to verify the analytical one. Numerical calculations are carried out for the chosen family of plates. The values of the critical load obtained by the analytical and numerical methods are compared. The effects of the material properties of the core and the change of the plate radius on the critical load intensity are presented.

Characteristics of bifurcation and buckling load of space truss in consideration of initial imperfection and load mode

This study investigated characteristics of bifurcation and critical buckling load by shape imperfection of space truss,which were sensitive to initial conditions.The critical point and buckling load were computed by the analysis of the eigenvalues and determinants of the tangential stiffness matrix.The two-free-nodes example and star dome were selected for the case study in order to examine the nodal buckling and global buckling by the sensitivity to the eigen buckling mode and the analyses of the influence,and characteristics of the parameters as defined by the load ratio of the center node and surrounding node,as well as rise-span ratio were performed.The sensitivity to the imperfection of the initial shape of the two-free-nodes example,which occurs due to snapping at the critical point,resulted in bifurcation before the limit point due to the buckling mode,and the buckling load was reduced by the increase in the amount of imperfection.The two sensitive buckling patterns of the numerical model are established by investigating the displaced position of the free nodes,and the asymmetric eigenmode greatly influenced the behavior of the imperfection shape whether it was at limit point or bifurcation.Furthermore,the sensitive mode of the two-free-nodes example was similar to the in-extensional basis mechanism of a simplified model.The star dome,which was used to examine the influence among several nodes,indicated that the influence of nodal buckling was greater than that of global buckling as the rise-span ratio was higher.Besides,global buckling is occurred with reaching bifurcation point as the value of load ratio was higher,and the buckling load level was about 50%-70% of load level at limit point.